216 SIR ROBERT CHRISTISON, BART., ON FOSSIL TREES 
is colourless. When neutralised, or nearly so, and filtered direct into solution 
of ferridcyanide of potassium, a dark prussian-blue precipitate is at once formed 
abundantly ; but if the ferrocyanide be substituted, the precipitate is at first of 
the palest possible azure-blue, passing gradually to deep blue under exposure 
to the air. Farther, the hydrochloric solution, filtered into solution of carbonate 
of soda, yields a white precipitate ; but if nitric acid be substituted for the 
hydrochloric acid to dissolve the fossil, the precipitate is of a dark ochre colour. 
Hence it follows that the fossil contains iron entirely in the state of protoxide. 
Its quantity was ascertained with sufficient approximation by throwing it 
down in the form of peroxide by adding ammonia to the nitric acid solution, 
acting on the washed precipitate with potash solution to remove a little alumina, 
and rendering the peroxide anhydrous at a full red-heat. 
When the potash solution, obtained by the last part of the preceding process, 
contained alumina, which, however, was not always the case, the alumina was 
separated by heating the solution after the addition of hydrochlorate of am- 
monia. When the proportion of alumina was to be ascertained precisely, the 
alumina and peroxide of iron were thrown down from the nitric acid solution 
by precipitated carbonate of baryta instead of ammonia. 
The nitric acid solution of the fossil, deprived of oxide of iron and alumina 
by ammonia, yields an abundant precipitate of white oxalate of lime on the 
addition of oxalate of ammonia. The lime was estimated in the usual way. 
The filtered solution when treated with phosphate of soda, more ammonia — 
being first added if judged necessary by the odour, yielded an abundant pre- 
cipitate of crystallised phosphate of magnesia and ammonia, from which the 
amount of magnesia was estimated as usual. 
All the araucarious fossils of Craigleith were found to present the same 
ingredients on being subjected to analysis. Some crude trials having led me 
to suspect that the proportion also of these ingredients might be the same in 
all of them, it was at first my intention to submit them all to careful numerical 
analysis. But, as subsequently several of the ingredients proved to vary con- 
siderably in proportion in the same fossil, the expectation of obtaining an exact 
ratio was necessarily given up. The Charcoal varied from 2°9 to 3:4, 49, and 
even 7‘0 per cent. This variation depends upon whether the fragment used 
may happen to contain small cavities filled with charcoal, or, on the contrary, 
masses of fossilising matter in radiating crystals. The proportion 2°9 was 
obtained from a lump of No. 6 fossil, weighing almost a pound. At this rate ~ 
the 36 feet of No. 5, in the British Museum, will contain rather more than a 
ton of charcoal. The iron estimated in the form of Carbonate of Protoxide of 
Tron has varied from 14:0 to 28-0 per cent. The circumstances regulating its 
proportion were not indicated in any of my analyses. The Carbonate of Lime — 
has amounted on an average to 60 per cent., and the Carbonate of Magnesia to 

